The present invention relates to integrated circuit power supply techniques for minimizing power consumption. More particularly, the present invention relates to generating a voltage supply by means of a circuit resident within a first integrated circuit, for powering additional peripheral chips, such as memory devices that operate at both high and low voltages.
In conventional electronic systems using a plurality of integrated circuits (ICs) it is typical to use a common voltage supply for each IC. For example these systems are typically built by grouping together and using only ICs of the 5 V or the 3 V type. This is done in order to simplify the system by reducing the power supply and wiring requirements inherent in a multiple supply design.
However, in low-power microcomputer systems, a problem exists with respect to segregating ICs by their power supply requirements. Many low-power microcomputers are designed to operate with a 3 V power supply so that they can be driven by one lithium cell, but generally available memory devices are typically designed for operation with a 5 V power supply. In a low-power electronic apparatus such as a battery-powered electronic notebook in which a microcomputer and an external memory device are combined, a power supply comprised of a pair of lithium cells connected in series is needed to provide the greater than 3 V power supply required by the memory. Therefore, in such an apparatus, current consumption is larger than that in a similar apparatus operated from a 3 V supply since the current used is a function of the voltage supply magnitude. As a consequence of higher power operation the life of batteries are shortened.
Additionally, most ICs of the 5 V type have an operating voltage specification of 5 V.+-.10%. When using a pair of lithium batteries in series it is possible to produce a supply voltage of up to 7 V. Therefore, it has been necessary to provide a circuit for regulating the supply voltage, in a two battery system, to a value within the operating voltage range of these ICs. This regulator circuit is typically a separate IC. Use of a separate regulator IC is burdensome because the system becomes larger, and more costly to manufacture.
One approach to providing appropriate voltages without using a second battery cell has been to add a DC-DC converter IC to the system. The DC-DC converter can provide the voltage required by peripherals such as RAMs. However there are several problems with this approach. First, the additional DC-DC converter IC limits miniaturization of the system housing. Second, this additional chip increases manufacturing costs. Third, when the DC-DC converter output is used to power a peripheral chip, interfacing between chips with different supply voltages leads to a mismatch in logic levels. Fourth, there is a diode leakage pathway between the two voltage supply nodes which gives rise to battery-draining parasitic currents.
Any approach that requires more battery cells or more ICs means that miniaturization of the housing becomes difficult.
Therefore a need exists in low-power systems, for a means to combine ICs having different power supply requirements, with only one low voltage supply, such as a battery, in the system, while simultaneously eliminating the need for costly additional components that consume space and power. There further exists a need for a means to interface circuits having different logic level voltages while still ensuring noise margin.